This application relates to the field of radio frequency identification tags including, but not limited to, a radio frequency identification tag system using tags arranged for coupling to ground.
Radio frequency identification tags and radio frequency identification tag systems are known, and find numerous uses. For example, radio frequency identification tags are frequently used for personal identification in automated gate sentry applications protecting secured buildings or areas. Information stored on the radio frequency identification tag identifies the person seeking access to the secured building. Older systems require the person accessing the building to insert or swipe their identification tag into or through a reader for the system to read the information from the identification tag. A radio frequency identification tag conveniently reads the information from the radio frequency identification tag at a small distance using radio frequency (RF) data transmission technology eliminating the inserting or swiping operation. Most typically, the user simply holds or places the radio frequency identification tag near a base station, which is coupled to a security system securing the building or area. The base station transmits an excitation signal to the radio frequency identification tag that powers circuitry contained on the radio frequency identification tag. The circuitry, responsive to the excitation signal, communicates the stored information from the radio frequency identification tag to the base station, which receives and decodes the information. The read information is communicated to the security system and, if appropriate, access is granted to the individual.
A typical technology for powering and reading a radio frequency identification tag is inductive coupling or a combination of inductive power coupling and capacitive data coupling. Inductive coupling requires incorporating a coil element into the radio frequency identification tag. The coil element is excited (or xe2x80x9cenergizedxe2x80x9d) by an excitation signal from a base station to provide power to the radio frequency identification tag circuitry. The radio frequency identification tag coil, or a second tag coil, may be used to transmit and receive information between the radio frequency identification tag and the base station. Inductive coupling technology is relatively expensive, particularly for applications where it may be desirable to have a disposable radio frequency identification tag such as in an inventory management application. Radio frequency identification tags relying on inductive coupling are also sensitive to orientation of the radio frequency identification tag with respect to the base station since the field created by the excitation signal must intersect the coil element at substantially a right angle for effective coupling. Furthermore, read ranges for inductively coupled devices are generally on the order of several centimeters. Longer read distances are desirable, and for certain applications such as electronic animal identification, baggage tracking, parcel tracking and inventory management applications, are necessary.
Other radio frequency identification tag technologies include magnetically coupled, magnetically and electrostatically coupled and dipole coupled electrostatic technologies. While offering certain performance enhancements, and in some cases cost advantages, over inductive coupling technology, read ranges with these other technologies can be limited. For example, in an article surveillance system for books, compact disks (CD) and other related media, it is necessary to read the radio frequency identification tag as it passes through a standard doorwayxe2x80x94generally about 90 centimeters (cm). Similarly, because of the vast differences in sizes of parcels and baggage an ability to read the radio frequency identification tag at a substantial distance is imperative. As will be further appreciated orientation of the radio frequency identification tag with respect to the base station can not be prearranged, and therefore, can not be allowed to substantially effect read distances. Each of the mentioned technologies tends to be overly orientation sensitive.
Thus, there is a need for an improved radio frequency identification tag system.